JBL 2445_46 frq.response

[ivica]

I have a pair of 2445 driver with 2446 ribbed membrane. measuring freq.response i have realized that both have deep notch "hole" about 3kHz ( about 15dB deep and say width about 1kHz/-15dB ). The picture is the same with an other driver too.
Is there any explanation or experience about such bad behavior of 2445?
It was 2311 JBL horn mounted on the drivers.

[1audiohack]

Hi ivica;

Was it mouted in a baffle or free standing in open air?

With the 2308 lense or without?

Without a baffle and lense it may not be well behaved.

[1audiohack]

Well hmmm;

I just measured one of my 2445's (with a 2445 diaphragm) with no horn at all, then with a 2311, and then with a 2311 and a 2308, standing up on the bench with no baffle.

With no horn at all I get an 11dB dip at 1328Hz but nothing like you are seeing.

Tomorrow I will baffle it and see what it looks like.

[lgvenable]

Audiohack..a 2445 with an aluminum diaphragm correct?

[1audiohack]

Nope, the stock D16R2445 made from Ti with diamond surround.

ivica if it would help I have a pair of 2226's that I could measure if you think it will help you. I will have to pull them out of another system to do it, and I belive they would sweep the same as the 2445's however.

[ivica]

Hi ivica;

Was it mouted in a baffle or free standing in open air?

With the 2308 lense or without?

Without a baffle and lense it may not be well behaved.

I have measured with baffle with almost the same results. I have not measure with lenses, I will do in next days, but I do not expect anything much difference. What is interesting is that I have done measurements with another not JBL horns, but the behavior around 3kHz is almost the same. I wonder that may be interaction of the 2445 internal horn-mouth (49mm- what corresponds to Lambda/2 of around 3kHz) as a kind of cancellation around Lambda/2.
My experience with 2420/21 (mouth around 25mm) has notch deep -6~8dB around 5kHz, but here with 2445 deep is too much.

[ivica]

Audiohack..a 2445 with an aluminum diaphragm correct?
I have put 2446/2450 Ti membrane (ribbed), because original had gone out, but as have seen from other experiences they have not any problem about.

[ivica]

Audiohack..a 2445 with an aluminum diaphragm correct?
Mine 2445 original membrane had gone out, so I put new original JBL 2446/2450
(16 Ohms) Ti "ribbed" membrane.

[ivica]

Nope, the stock D16R2445 made from Ti with diamond surround.

ivica if it would help I have a pair of 2226's that I could measure if you think it will help you. I will have to pull them out of another system to do it, and I belive they would sweep the same as the 2445's however.

As I understand 2226 is BASS, I believe that you think about 2426 ( 1 inch mouth). I have done the same measurements with mine 2420 with Ti membrane ( similar to 2421Ti). It has noticeable notch around 5kHz ( about 6~8 dB deep), but not 15dB as I have for 2445

[ivica]

Hi ivica;

Was it mouted in a baffle or free standing in open air?

With the 2308 lense or without?

Without a baffle and lense it may not be well behaved.

I have done with and without baffle, but without 2308 lenses. I will do the measurements with lenses too one in next days, but I do not expect large improvement.

[grumpy]

I assume the measurement is on-axis, but what distance from the horn (baffle surface) is
the measurement made?

[1audiohack]

As I understand 2226 is BASS, I believe that you think about 2426 ( 1 inch mouth).


Sorry I meant to say I also have a pair of 2446's (with the original diaphragms), I could measure one of them also, they are in service so I would have to pull one out to measure it. I believe it will measure the same as the 2445 however.

[ivica]

I assume the measurement is on-axis, but what distance from the horn (baffle surface) is
the measurement made?
Yes, on axis measurements. I Did on about 1.2m and about 0.4m, but with almost the same results

[ivica]

Sorry I meant to say I also have a pair of 2446's (with the original diaphragms), I could measure one of them also, they are in service so I would have to pull one out to measure it. I believe it will measure the same as the 2445 however.
Nice if you can measure it and send the measurements: [email protected]

[ivica]

Finally I have measured it with "lens" but unfortunately with almost same result
If ant help.

[withTarragon]

In my experience a notch that narrow and deep is usually due to a "bounce" somewhere. Since you get it at different distances, it is probably not a floor bounce. The obivous question (and you probably already know this) is whether there is a hard surface about 2-4 inches from the mic.

I have measured 2446's mounted on tractrix horns (Klipsch) and CD horns (Electro-voice HP series) and I have not seen that behavior.

Just an oddball possibility, is the seal between the driver and horn nice and snug (is there a gasket)?

BTW, I am a fan of the 2446. It is a great driver, but you need to stay from after-market diaphragms.

-Tom

[Earl K]

Also, inexplicable notches can be caused by a poorly fitted diaphragm .

Heres' one such example .

http://www.audioheritage.org/photopost/data//500/Radian_in_802_or_902_Altec_1.PNG

I've never had any success in getting a proper fit with this one Radian diaphragm .
The pic shows separate attempts on two different Altec driver bodies ( an 802 & a 902 ) .

<> cheers

[ivica]

unfortunately I have done a lot of measurements in different positions using even several measuring methods (one of them is my own based on spread spectrum techn.), but all of them including well known TrueRTA "recognized" the mentioned deep notch about 3kHz. I want to emphasize that almost the same character can be find on another 2445 driver (I have). Reading some help docs for AkAbak simulation software I realized that may be some small change in the volume of the cavity where the voice coil is accommodated can produce such deep notches. I did mine easy simulation using mentioned AkAbak (fig.3) and I can easily get such notches. That give me some "idea" that there exist some kind of cavity that interact with the diaphragm.
May be the main reason is that I have used D16R2450 (diaphragm for 2446 ) instead of D16R2445, or there is something else.



-Tom[/QUOTE]

[ivica]

unfortanety I can not attach pictures now.





-Tom[

[ivica]

Also, inexplicable notches can be caused by a poorly fitted diaphragm .

Heres' one such example .



I've never had any success in getting a proper fit with this one Radian diaphragm .
The pic shows separate attempts on two different Altec driver bodies ( an 802 & a 902 ) .

<> cheers


If mentioned notch can be neglected (#@#$%&), the response on both 2445 drivers are very similar, of course not absolute identical, so it is expectable that there would some differences but mentioned notch is my 'vital' problem.

[Earl K]

Mine 2445 original membrane had gone out, so I put new original JBL 2446/2450 (16 Ohms) Ti "ribbed" membrane.

Are you positive that those replacement diaphragms you bought are original JBL equipment and not just some counterfeit Chinese/Thai junk ?

<> cheers

[ivica]

Are you positive that those replacement diaphragms you bought are original JBL equipment and not just some counterfeit Chinese/Thai junk ?

<> cheers

I buy them from local authorized JBL dealer (mentioned on JBLPRO site as responsible for my country) . Box seem original, and concerning lot of marks on voice coil former it seems that it is from JBL, but nowadays nobody is sure, especially for JBL that is closing most of their plants and mainly keeping sales dept. in USA....but such is known story for many other not "profitable" company.:crying:

[Earl K]

I buy them from local authorized JBL dealer (mentioned on JBLPRO site as responsible for my country) . Box seem original, and concerning lot of marks on voice coil former it seems that it is from JBL, but nowadays nobody is sure, especially for JBL that is closing most of their plants and mainly keeping sales dept. in USA....but such is known story for many other not "profitable" company.:crying:

Tom,

Thanks for answering that queston . Your diaphragms certainly seem legitimate .

I'm not aware of any known ( official JBL ) restriction against putting a D16R2450 diaphragm into the 2445 body .

For now, I guess I'm out of ideas .

<> cheers

ps ; One last idea, have someone else measure a single unit of yours ( with a 2311 horn ) and see if they can confirm your findings .

[ivica]

Tom,

Thanks for answering that queston . Your diaphragms certainly seem legitimate .

I'm not aware of any known ( official JBL ) restriction against putting a D16R2450 diaphragm into the 2445 body .

For now, I guess I'm out of ideas .

<> cheers

ps ; One last idea, have someone else measure a single unit of yours ( with a 2311 horn ) and see if they can confirm your findings .

That "restriction" of putting a D16R250 into 2445 for sure would not "smash" phasing plug for sure :(, but really such behavior near 3kHz was not expected for me.:banghead:

[grumpy]

I have examples of both the 2445 motor and 2446 diaphragm at home.
If I remember to, I'll put them together with a 2311 and independently measure
with and without the 2308 lens.

I seem to recall doing this before (different horn, no lens) and not noticing
such problems, but I can't find the files, so I might as well duplicate the
setup as closely as possible.

-grumpy

[ivica]

I have examples of both the 2445 motor and 2446 diaphragm at home.
If I remember to, I'll put them together with a 2311 and independently measure
with and without the 2308 lens.

I seem to recall doing this before (different horn, no lens) and not noticing
such problems, but I can't find the files, so I might as well duplicate the
setup as closely as possible.

-grumpy

That would be nice:bouncy:, so may be the mystery will be "uncovered"
Thanks in advance

I have now my figure and AkAbak script file. What is importanat that the mentioned notch at 3kHz can be simulated as
a cavity around voice coil and its path ( Ha, ds and ls in attached script file)

[grumpy]

status: 2445 and 2441 assembled. Need to fit 2446 diaphragm and test.

I would have gotten it done but my daughter had a tire blow out on her way to work
yesterday evening... she's fine. I'll still get to the testing.

[ivica]

I have examples of both the 2445 motor and 2446 diaphragm at home.
If I remember to, I'll put them together with a 2311 and independently measure
with and without the 2308 lens.

I seem to recall doing this before (different horn, no lens) and not noticing
such problems, but I can't find the files, so I might as well duplicate the
setup as closely as possible.

-grumpy
Here are some measurement done with 3133 compatible network
with 2445 body with D16R2450 Diaphragm and 2311&2308 horn-lens,
and for comparison measurements of 2421 with its 2307&2308 horn-lens

iti s added (on one measurement) Beyma CP21F UHF driver, unfortunately I have no 2405

[ivica]

status: 2445 and 2441 assembled. Need to fit 2446 diaphragm and test.

I would have gotten it done but my daughter had a tire blow out on her way to work
yesterday evening... she's fine. I'll still get to the testing.

I have seen some measurements that other member (4313B (http://www.audioheritage.org/vbulletin/member.php?15-4313B) ) did with 2445 body and D16R2450
diaphragm ( as is in 2446 driver) and everythink is perfect

[grumpy]

good to have that 2421 measurement for comparison (not likely to be an inherent
measurement problem). I'm happy to do another independent measurement and
it would be good to dust off the test gear, so no problem :) I will not be using a
complete network though (3133 or otherwise), just a large capacitor.

[ivica]

good to have that 2421 measurement for comparison (not likely to be an inherent
measurement problem). I'm happy to do another independent measurement and
it would be good to dust off the test gear, so no problem :) I will not be using a
complete network though (3133 or otherwise), just a large capacitor.

For sure just large capacitor would be OK, to protect driver from LF. I did my first measurement without network, just in order to be sure that there was no inherent measurement problem.
Your work would be very informative, and any suggestion is well come.

[ivica]

In my experience a notch that narrow and deep is usually due to a "bounce" somewhere. Since you get it at different distances, it is probably not a floor bounce. The obivous question (and you probably already know this) is whether there is a hard surface about 2-4 inches from the mic.

I have measured 2446's mounted on tractrix horns (Klipsch) and CD horns (Electro-voice HP series) and I have not seen that behavior.

Just an oddball possibility, is the seal between the driver and horn nice and snug (is there a gasket)?

BTW, I am a fan of the 2446. It is a great driver, but you need to stay from after-market diaphragms.

-Tom

The mic was mounted about 1.5 m from ceiling and about 1.5m from speaker, no other reflective object near. That was my first "idea" that there was kind of 'reflective cancellation' due which would make about 5cm sound delay ( 3kHz ~ 10cm wave length). yesterday I have done measurements with 2421 (&2307) fixed on the same place as 2445 and there was no notch bear 3kHz, so "ambient" influences is out of.....

I do not know is there any special part which is missed....

[ivica]

Tom,

Thanks for answering that queston . Your diaphragms certainly seem legitimate .

I'm not aware of any known ( official JBL ) restriction against putting a D16R2450 diaphragm into the 2445 body .

For now, I guess I'm out of ideas .

<> cheers

ps ; One last idea, have someone else measure a single unit of yours ( with a 2311 horn ) and see if they can confirm your findings .


As you can seen on this thread, i have done measurements with 2421 with 2307 on the same place as 2445 with 2311, i either case with 2308 lens and with 2421 everything is OK, with expect able response.

[ivica]

Also, inexplicable notches can be caused by a poorly fitted diaphragm .

Heres' one such example .



I've never had any success in getting a proper fit with this one Radian diaphragm .
The pic shows separate attempts on two different Altec driver bodies ( an 802 & a 902 ) .

<> cheers


Some differences are expect-able between the drivers and diaphragms but I have almost the same behavior around 3kHz on either driver.

[ivica]

Sorry I meant to say I also have a pair of 2446's (with the original diaphragms), I could measure one of them also, they are in service so I would have to pull one out to measure it. I believe it will measure the same as the 2445 however.

I am very restless to see your data, even I think that 2446 is much better then 2445.

[grumpy]

graphs as promised, noting that below 10KHz, in a 2445 body, the difference between
diaphragm responses is minimal. Above 10KHz, there -appear- to be some resonances added
(2446 'ribs') to effectively extend the response. I see no deep/wide notch, and see no need
to attach a 2308 lens and remeasure (there is nothing to mitigate). At this time I did not
try a 2446 body to see if the "Coherent Wave" phase plug improves possible summation/
cancellation issues in the 11-15KHz range.

47110

[grumpy]

As the plots of your drivers appear consistent from unit to unit and diaphragm to diaphragm,
I can only think that either both drivers or both diaphragms are self-consistent, and perhaps
precision-machined (just not correctly), non-JBL "copies" :dont-know: ... or JBL units that are somehow
damaged in a similar fashion.

Can you compare some of the specs with other measurements?:

http://www.jblpro.com/pub/components/2446.pdf

http://www.lansingheritage.org/html/jbl/specs/pro-comp/2445h.htm

[ivica]

graphs as promised, noting that below 10KHz, in a 2445 body, the difference between
diaphragm responses is minimal. Above 10KHz, there -appear- to be some resonances added
(2446 'ribs') to effectively extend the response. I see no deep/wide notch, and see no need
to attach a 2308 lens and remeasure (there is nothing to mitigate). At this time I did not
try a 2446 body to see if the "Coherent Wave" phase plug improves possible summation/
cancellation issues in the 11-15KHz range.

47110

What a nice and valuable work. :applaud:
Everything is under expect-able tolerance. This second pole "resonance" is even expected and explained in the JBL Tehn.Notes Vol.1 no.8 ,
JBL_Durbin Patanet no.4324312 and in Murray_Durbin JASE paper "Three-Dimensional Diaphragm Suspensions for Compression Drivers"-1979-1980.
Unfortunately I can not reach such good results.
Yesterday night I open both 2445 divers, to see if anything can be a reason for such unexpected behaviors, but everything seems to be on the right place. The diaphragm is fixed tightly by 8 screws. When the screws are removed you need some amount of force to take the diaphragm assembly out of the body. The diaphragms are in perfect condition without any visible damages.

Mechanical grave for accepting diaphragm assembly does not allow any "radial" misalignment of the diaphragm. Rotation of the assembly seems that does not give any audible differences.
Phasing plug is fixed firmly. On the plyg there are about (as remember) 6-six (concentric openings). Everything is clean......:crying:, so now I have no ANY ideas., but any help is well come . Say: photos of the open 2445 body, your 2446 diaphragm (specially from "bottom side"). What for me is unexpected is relatively short voice coil (former) about 4mm......
Ivica

[grumpy]

I'll take and post some driver and diaphragm pictures this evening, as well as
measuring the voice coil former length... 4mm seems much too short (from memory).

[ivica]

I'll take and post some driver and diaphragm pictures this evening, as well as
measuring the voice coil former length... 4mm seems much too short (from memory).

well, may be measured from the diaphragm itself is 5mm maximum 6mm

[grumpy]

Meanwhile, here are some images that may help:
http://www.speakerrepair.com/mm5/merchant.mvc?Screen=PROD&Product_Code=10-257

[4313B]

Yesterday night I open both 2445 divers, to see if anything can be a reason for such unexpected behaviors, but everything seems to be on the right place. The diaphragm is fixed tightly by 8 screws. When the screws are removed you need some amount of force to take the diaphragm assembly out of the body. The diaphragms are in perfect condition without any visible damages.

Mechanical grave for accepting diaphragm assembly does not allow any "radial" misalignment of the diaphragm. Rotation of the assembly seems that does not give any audible differences.
As nice and tight as it all seems it's only a ruse. The eight screws should be tightened while feeding a 350 Hz test tone (4-inch diaphragms, 500 Hz for 1.75-inch diaphragms) into the compression driver. Once the screws are tight enough to mitigate the various resonances a slow sweep from 350 Hz to 20 kHz is made to ensure that there are no resonances at any other frequencies. It can take some time to get a diaphragm properly torqued down.

Post a picture of the diaphragm installed in the core, preferably with the backcap wires still connected to the diaphragm. The wires should stay carefully routed around the outsides of the diaphragm ring when the backcap is closed (and there shouldn't be anything in contact with the diaphragm, for instance, rotted foam).

How does the impedance curve look?

[ivica]

Meanwhile, here are some images that may help:
http://www.speakerrepair.com/mm5/merchant.mvc?Screen=PROD&Product_Code=10-257

Yes, the box and diaphragm looks similar to mines, and the prices too :(

[ivica]

As nice and tight as it all seems it's only a ruse. The eight screws should be tightened while feeding a 350 Hz test tone (4-inch diaphragms, 500 Hz for 1.75-inch diaphragms) into the compression driver. Once the screws are tight enough to mitigate the various resonances a slow sweep from 350 Hz to 20 kHz is made to ensure that there are no resonances at any other frequencies. It can take some time to get a diaphragm properly torqued down.

Post a picture of the diaphragm installed in the core, preferably with the backcap wires still connected to the diaphragm. The wires should stay carefully routed around the outsides of the diaphragm ring when the backcap is closed (and there shouldn't be anything in contact with the diaphragm, for instance, rotted foam).

How does the impedance curve look?

while installing the diaphragm I tried do my best
first cleaning the voice-coil gap in 2445 body. I have done that in the way that is suggested to be done while changing diaphragm on 2405 ( presented on:

http://www.youtube.com/watch?v=POHs1n_PXX4

as:"JBL 2404, 2405, 077 and 075, 2402 Installation Video:" from SoundSpeakerRepair.com
). sweeping tons....and could not recognize any imperfection in tones. Of course the back-cap wires were carefully arranged out of the diaphragm assembly. I will try to make a photo with "half removed back-cap". I wonder how almost the same problem is present to both drivers. If some imperfection in work was present on one driver, there is low level of probability that the same is present to the other, but may be I have make some systematic ERROR :blink: , but what ????

[grumpy]

voice coil depth (from underside of diaphragm 'diamond' surround to edge of former)
measured at 4.5-4.6mm, best I could determine.

pics. D16R2450


4712847129471304713147132

[4313B]

I will try to make a photo with "half removed back-cap".No need. It sounds like you know how to put them together properly.

[Earl K]

No need. It sounds like you know how to put them together properly.

Well Tom,

It's still a mystery why your two new diaphragms don't perform correctly .

I suggest that you take both back to your JBL dealer and ask him to install them into either a 2450/1 or 2446/7 driver ( from his own stock ) . Pay him to do it , if that is what it takes to get this done .

Then take some response measurements ( at the JBL dealers shop ) of the diaphragms fitted into the proper drivers ( use your 2311 horn . This should prove ( or disprove ) that your diaphragms can be made to work correctly .

It's possible ( maybe unlikely ) , those diaphragms just won't ever fit into your ( 2 ) 2445 drivers .

- I have a new D8R2450SL diaphragm that just won't fit into any of the ( 8 ) 2440/1 drivers that I own . This diaphragm cost me @ $ 300.00 Cdn, eight or nine years back .
- I wish I had followed similar advice to confirm ( or not ) if it was a manufacturing defect that prevents a proper fitup from happening with any of my drivers .
- This diaphragm seems to be "tight" in the gap, implying to me that it's a bit wide in the voice-coil windings .
- If I had been able to prove it couldn't be properly mounted into a JBL dealers' 2446, I might have been able to get a no-cost replacement ( based on the discretion of the dealer ) .
- It was a somewhat expensive mistake on my part to not findout why this diaphragm won't work with my stuff .

Anyways, there's one route to think about .


<> cheers EarlK

[ivica]

Well Tom,

It's still a mystery why your two new diaphragms don't perform correctly .

I suggest that you take both back to your JBL dealer and ask him to install them into either a 2450/1 or 2446/7 driver ( from his own stock ) . Pay him to do it , if that is what it takes to get this done .

Then take some response measurements ( at the JBL dealers shop ) of the diaphragms fitted into the proper drivers ( use your 2311 horn . This should prove ( or disprove ) that your diaphragms can be made to work correctly .

It's possible ( maybe unlikely ) , those diaphragms just won't ever fit into your ( 2 ) 2445 drivers .

- I have a new D8R2450SL diaphragm that just won't fit into any of the ( 8 ) 2440/1 drivers that I own . This diaphragm cost me @ $ 300.00 Cdn, eight or nine years back .
- I wish I had followed similar advice to confirm ( or not ) if it was a manufacturing defect that prevents a proper fitup from happening with any of my drivers .
- This diaphragm seems to be "tight" in the gap, implying to me that it's a bit wide in the voice-coil windings .
- If I had been able to prove it couldn't be properly mounted into a JBL dealers' 2446, I might have been able to get a no-cost replacement ( based on the discretion of the dealer ) .
- It was a somewhat expensive mistake on my part to not findout why this diaphragm won't work with my stuff .

Anyways, there's one route to think about .


<> cheers EarlK

That is good proposal, but here in Serbia, such relationship with the barn company support is almost 'science-fiction". I was happy that I can get (I believe) original diaphragm, and such
complicated investigation is out of any expectation ( sorry for my bad English).
I wonder, may be, my drivers (I have bought them as second hand) have some systematic malfunctions, but lookig from out side I can not see.
I have make some photos, so you can see in this thread.

[ivica]

voice coil depth (from underside of diaphragm 'diamond' surround to edge of former)
measured at 4.5-4.6mm, best I could determine.

pics. D16R2450


4712847129471304713147132

yes, on mine diaphragm almost the same, but the stickers are from inside of teh assembly. fixing the voice coil is done almost on teh same way

[ivica]

Well Tom,

It's still a mystery why your two new diaphragms don't perform correctly .

I suggest that you take both back to your JBL dealer and ask him to install them into either a 2450/1 or 2446/7 driver ( from his own stock ) . Pay him to do it , if that is what it takes to get this done .

Then take some response measurements ( at the JBL dealers shop ) of the diaphragms fitted into the proper drivers ( use your 2311 horn . This should prove ( or disprove ) that your diaphragms can be made to work correctly .

It's possible ( maybe unlikely ) , those diaphragms just won't ever fit into your ( 2 ) 2445 drivers .

- I have a new D8R2450SL diaphragm that just won't fit into any of the ( 8 ) 2440/1 drivers that I own . This diaphragm cost me @ $ 300.00 Cdn, eight or nine years back .
- I wish I had followed similar advice to confirm ( or not ) if it was a manufacturing defect that prevents a proper fitup from happening with any of my drivers .
- This diaphragm seems to be "tight" in the gap, implying to me that it's a bit wide in the voice-coil windings .
- If I had been able to prove it couldn't be properly mounted into a JBL dealers' 2446, I might have been able to get a no-cost replacement ( based on the discretion of the dealer ) .
- It was a somewhat expensive mistake on my part to not findout why this diaphragm won't work with my stuff .

Anyways, there's one route to think about .


<> cheers EarlK
I put some photos

[ivica]

[QUOTE=grumpy;293749]voice coil depth (from underside of diaphragm 'diamond' surround to edge of former)
measured at 4.5-4.6mm, best I could determine.

pics. D16R2450


Thanks for teh nice photos. As I told you the voice coil is relatively unxpectable "short".
On my mind one idea "come", may be my magnet is weak , I have no ide how to measure the
magnetic field in the gap (off course I have no specila measuring equipmemnt )

[ivica]

[QUOTE=grumpy;293749]voice coil depth (from underside of diaphragm 'diamond' surround to edge of former)
measured at 4.5-4.6mm, best I could determine.

pics. D16R2450

One 'interesting' thing while cleaning the voice coil gap, I realized that this narrow gap is VERY DEEP about 30mm> While pitting this in AkAbak simulator this small box can make the very deep notch around the frequency we are toking about.
Here is AkAbak Script and its response.
what is iportant deep notch around 3kHz and smaller here on 9kHz (on measured on 10kHz),
Black line on attached figure,
but if depth of the voice coil gp is reduced from 30mm to 8mm then the figure would be different-red line

[Earl K]

voice coil depth (from underside of diaphragm 'diamond' surround to edge of former)
measured at 4.5-4.6mm, best I could determine.



One 'interesting' thing while cleaning the voice coil gap, I realized that this narrow gap is VERY DEEP about 30mm> .

- While pitting this in AkAbak simulator this small box can make the very deep notch around the frequency we are toking about.
- Here is AkAbak Script and its response.
- What is important ( is the at ) deep notch around 3kHz and (the ) smaller here on 9kHz (on measured on 10kHz),
Black line on attached figure,
- But if depth of the voice coil gp is reduced from 30mm to 8mm then the figure would be different-red line

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=47187&stc=1&d=1282552315

- Maybe it's nothing but , JBL doesn't use the type of binding(connection) posts shown in the above picture . That type was commonly used by P-Audio copies of the 2445 driver .
- Plus, the black connector is supposed to be on the left-hand side .
- They could have been switched by someone ( so as to follow normal color-coding /polarity conventions, I suppose ) .

The 1.18" depth of the gap/top-plate ( which you just mentioned ) seems wrong for a bonafide JBL .
- Are you sure of that measurement ?

- Anyways, you need to have someone with a 2445 driver measure the depth of the gap ( I don't own any 2445 driver ) so that you can compare to what you have .

<> cheers

[ivica]

[QUOTE=ivica;293896]



JBL doesn't use the type of binding(connection) posts shown in the above picture . That type was commonly used by P-Audio copies of the 2445 driver .

The 1.18" depth of the gap/top-plate ( which you just mentioned ) seems wrong for a bonafide JBL .
- Are you sure of that measurement ?

- Anyways, you need to have someone with a 2445 driver measure the depth of the gap ( I don't own any 2445 driver ) so that you can compare to what you have .

<> cheers

May be your right that this is bad copy of 2445 driver. In order to measure the 'depth' of voice coil gap I haev used a strip of hard paper and pushed it in until reached the bottom. May be there is an error of 1mm but for sure about 30mm. I will try to measure the width (under magnet pole plate). May be it is wider than the gap at the top. The problem is that if I would "discover" a large cavity under pole plate. How to "fill-in" such cavity, and what effect such experiment would produce. Concerning the AkAbak simulation, such cavity can introduce such notch about 3kHz. Generally the problem for such experiments is that you can not disassemble the driver with "home equipment"

[grumpy]

I'm 99.999999999% sure that's not a 2445 or a JBL driver at all.

That side view and the phase plug pictures are not what I would expect.

You might want to read through this thread:

http://www.audioheritage.org/vbulletin/showthread.php?28776

[ivica]

I'm 99.999999999% sure that's not a 2445 or a JBL driver at all.

That side view and the phase plug pictures are not what I would expect.

You might want to read through this thread:

http://www.audioheritage.org/vbulletin/showthread.php?28776

Yes, I have red that before. I am afraid that mines are some copy (unfortunately bad)

[grumpy]

It is still interesting (at least to me), that your AkAbak model assumptions seem to correspond to the "problem" driver behavior.

At least one mystery was solved.

[ivica]

It is still interesting (at least to me), that your AkAbak model assumptions seem to correspond to the "problem" driver behavior.

At least one mystery was solved.

Well, to be honest, in AkAbak software there are several examples where I have find the example for model of compression driver and that was starting point.
If you would like to "experiment" on computer I suggest:

http://www.randteam.de/_Software/AkAbak/Download-AkAbak.html

where you can download AkAbak....

[robertbartsch]

...someone went to extraordinary measures to copy this driver and, from the visual inspections, it was diffucult for the experts here to identify them as fakes.

OK, so what have we learned from this?

1. Harman to Houston: "We have a problem!"

2. The technology that is necessary to manufacture modern JBL drivers ("knock-offs") is not as complex as one might initially think.

3. Thre is a significant cost advantage to manufacture these in Asia (??) Vs the USA - otherwise Asian cheats (??) would not do this. (Remember - Toyota and Honda "copied" GM and Ford in the 1960s)

4. Someone is likely to use the experience they gained in making the knock-offs to develop new OEM products that are competitive in the marketplace with JBL and, eventually that surpass the performance of JBL.

5. The participants in today's world economy do not always play fair.

6. If I'm the CEO of Harman, I need to keep close tabs on what is happening in the marketplace and to take appropriate action to avoid being uterly CRUSHED!

[robertbartsch]

...one other thing...

I'm going home tonight and I plan to check my pair of 2445Js to see if they are real. When I installed a new pair of OEM 8 ohm frames about one year ago, I remember not being able to see down the throat to the phase plug, so I should be OK.

...This blows!

[1audiohack]

You missed a couple of things in this thread Robert,

The knock off driver doesn't work well, that's the reason for this thread. And the fact it does not perform well delights me! The fact that someone (ivica) bought them unknowingly and in reality has been cheated sorrows me.

Also it was not difficult to identify it as a knock off, at all, when I saw a picture of it I knew what it was right off as did others, and I am no expert.

You're right, it's cheaper to make them in Asia, but, as Warren Buffet rightly said, "Price is what you pay, value is what you get." So, are they of any value? They would not be to me. How inexpensive would they have to be for you to say, "Yeah, they suck, but they were cheap!

If they could not even duplicate the performance of an obsolete driver they had in their hands as a model, how do you think they will surpass JBL? And if they do surpass JBL in quality, who's fault would that be?



5. The participants in today's world economy do not always play fair.

No they don't, and I don't know if they ever did.

[robertbartsch]

You missed a couple of things in this thread ...

The knock off driver doesn't work well, that's the reason for this thread. And the fact it does not perform well delights me! The fact that someone (ivica) bought them unknowingly and in reality has been cheated sorrows me.

**************

I don't think I missed the fact that the "knock-off drivers" do not perform to JBL specs - surprise, surprise.

To me, the fact that the buyer was ripped-off is sad, however, some here might have missed the BIG picture. Someone went to the trouble to make a fairly exact copy of one of the best compression drivers on the market and that was done for a reason. My guess is that they did so to obtain manufacturing knowledge so they could eventually design their own drivers and compete in the marketplace with Harman.

I'm not an engineer, but I assume their shortfall in the knock-off was that they failed to copy the OEM phase plug exactly. Wow, I wonder how hard that would be to correct?

These drivers have been out of production for a while and the knock-off copies are not new either, so this indicates the "knock-off "problem" has been with us for a while. If I were Harman management, this would scare the cr@p out of me!

Most knock-offs like shoes, handbags, sports clothing, jewlery, ect. are made to undercut the seller/manufacturor of high-price luxury items. Considering these drivers are mostly used in professional installations like movie houses and sound reinforcement, I doubt that this was done to undercut JBL and that is why Harman should be very concerned.

[ivica]

You missed a couple of things in this thread Robert,

The knock off driver doesn't work well, that's the reason for this thread. And the fact it does not perform well delights me! The fact that someone (ivica) bought them unknowingly and in reality has been cheated sorrows me.

Also it was not difficult to identify it as a knock off, at all, when I saw a picture of it I knew what it was right off as did others, and I am no expert.

You're right, it's cheaper to make them in Asia, but, as Warren Buffet rightly said, "Price is what you pay, value is what you get." So, are they of any value? They would not be to me. How inexpensive would they have to be for you to say, "Yeah, they suck, but they were cheap!

.

Firstly to say, I was not so careful while buying mentioned "2445", because i have no idea that such thing is "attractive enough" to be copied, especially the driver were mounted on enormously large horns ( may be the horns are "fake" JBL 2360A ).
I am sure that the company making copy of the drivers has quite enough knowledge to understand what is important for audio quality compression driver. I do believe that they had made lot of measurements of their product before starting "mass" production. But after all, I can not understand two things: why they make so large 'cavity' in the voice coil 'circuits', because that it is "visible from the plain" that such construction would reduce the efficiency, and only very cheap ring made of plastic or aluminum would dramatically improve the characteristic of the driver, and the production price would increase insignificantly. and second, concerning the phasing-plug is the same story. The amount of the material is the same, and to copy the shape is very easy.

[ivica]

...someone went to extraordinary measures to copy this driver and, from the visual inspections, it was diffucult for the experts here to identify them as fakes.

OK, so what have we learned from this?

1. Harman to Houston: "We have a problem!"

6. If I'm the CEO of Harman, I need to keep close tabs on what is happening in the marketplace and to take appropriate action to avoid being uterly CRUSHED!

I think that Harman "couldn't care less" about JBL-pro products at all.:(

[ivica]

...one other thing...

I'm going home tonight and I plan to check my pair of 2445Js to see if they are real. When I installed a new pair of OEM 8 ohm frames about one year ago, I remember not being able to see down the throat to the phase plug, so I should be OK.

...This blows!

I believe that you are lucky and you have original 2445 frame,
but why you put 8 Ohms diaphragm frame instead of 16 Ohms ( yes larger current for the same voltage, but "Bl" factor less ), but that is only my curiosity.

[ivica]

It is still interesting (at least to me), that your AkAbak model assumptions seem to correspond to the "problem" driver behavior.

At least one mystery was solved.

If you have some amount of time you can see :
http://www.kozystudio.com/bu2bu2/fake/fake.htm
(of course with translation from Japanese) I can say "my diver in detail"
even on resposne there is a small notch at 3kHz, but because of the large horn
(jbl like 2380) sound at 1kHz 'mask' the rest

[ivica]

It is still interesting (at least to me), that your AkAbak model assumptions seem to correspond to the "problem" driver behavior.

At least one mystery was solved.

what is more interesting lot of expect-able problems around voice coil and cavity near
were mentioned in 1936 patent, US2037187 and later elaborated
http://www.aes.org/e-lib/browse.cfm?elib=2932
(unfortunately i can not download this document)

[robertbartsch]

Ivica:
When I bought my pair of 2445Js they came with original JBL diaphragms that were dated in the late 1980s I beleive. Anyway, since the frams were many years old, I decided to replace them and the other components in my planned system were 8 ohms so that was the logical choice.

I may have missed this in the earlier threads, but how did you obtain these drivers? Can you return them to the seller and request a refund since they are obvious fakes?

Good luck!

PS - Since a significant amount of revenues of Harman International are derived from JBL Professional equipment, I would have to say that JBL cares about their products and the knock-off problem.

[ivica]

Ivica:
When I bought my pair of 2445Js they came with original JBL diaphragms that were dated in the late 1980s I beleive. Anyway, since the frams were many years old, I decided to replace them and the other components in my planned system were 8 ohms so that was the logical choice.

I may have missed this in the earlier threads, but how did you obtain these drivers? Can you return them to the seller and request a refund since they are obvious fakes?

Good luck!

PS - Since a significant amount of revenues of Harman International are derived from JBL Professional equipment, I would have to say that JBL cares about their products and the knock-off problem.

Unfortunately the possibility to refund my expenses is near 0.00000001%
either for the drivers or the diaphragms, so that means I can put the diaphragms in to "picture frame" and "hang them on the wall" with all JBL stickers on them.
The driver may be i can use for "door bumpers" because they have very good preserved rubber surroundings around the magnet

May be I can sand an e-mail to JBL-pro dept. so that they can suggest me how to "upgrade" my fake-drivers to reach near original. May be JBL can offer me Phasing-plugs that can help.

[Maron Horonzakz]

I dont think JBL would touch them with a ten foot pole.,,, Its not there problem...Its your loss.

[louped garouv]

I dont think JBL would touch them with a ten foot pole.,,, Its not there problem...Its your loss.

they may be able to physically confirm that they are fakes/clones tho'
or tell the purchaser how to discern between the two.



:)

[tomee]

Unfortunately the possibility to refund my expenses is near 0.00000001%
either for the drivers or the diaphragms, so that means I can put the diaphragms in to "picture frame" and "hang them on the wall" with all JBL stickers on them.
The driver may be i can use for "door bumpers" because they have very good preserved rubber surroundings around the magnet

May be I can sand an e-mail to JBL-pro dept. so that they can suggest me how to "upgrade" my fake-drivers to reach near original. May be JBL can offer me Phasing-plugs that can help.

On the plus side, you do seem to have real JBL diaphragms, so all you need now are blown 2445s, which are not too hard to come by.

At first I was surprised to see that the fake had a redesigned phase plug, and a really poor one at that. But of course if it's not infringing on any patents etc. and it's simpler to make then JBL can't do anything about it. But, whoever put the JBL label on the back broke the law.

[ivica]

On the plus side, you do seem to have real JBL diaphragms, so all you need now are blown 2445s, which are not too hard to come by.

At first I was surprised to see that the fake had a redesigned phase plug, and a really poor one at that. But of course if it's not infringing on any patents etc. and it's simpler to make then JBL can't do anything about it. But, whoever put the JBL label on the back broke the law.

tomee:
what is 'interesting" for me is that the "phasing plug" has , say, equally distance annular input throats but with different width (smallest towards the center) and as can be seen from the picture with almost equally with of the 'mouth', what is expect-able trend concerning the rule: "percentage of area of mouth of each wave guide of total output area has to correspond to the percentage area of each input area"), on the other side mentioned "phasing plug" is 'connected to the "inverse" short conical horn while together with mentioned phase plug generate 'sound' wave front at the throat of the internally short horn. All in all it seems that someone had spent some time in calculating and projecting all this (I believe that it had been easier to copy some of JBL or others verified products).
On the other side under vice coil path there is enormously large cavity which is known as a potential 'notch generating problem' in driver response. May be at the beginning there was large amount of 'Ferrofluid', but as it is known such construction with open system would become full of dust and would block voice coil assembly after years of use.

for me it would be nice to find a pair of "blown" 2445, but where ?????:confused:

[ivica]

I dont think JBL would touch them with a ten foot pole.,,, Its not there problem...Its your loss.

Maron:

Yes, I think so, but I am sure that (or better to say: I would expect that) in JBL someone has to "track" JBL fake products in the world market, and nowadays, with Internet "support", it would be very easy to show on, here say, www.JBLPRO.com
site one page where all potential customers can see how 'fake product" look like....:eek:

[ivica]

I have decided to "fill-in" the large cavity under voice coil path, and the i will make new measurements to see what would happen. I expect that the efficiency would rise, and that the notch would move towards higher frequency, may be 'out of the interest'.:(

[ivica]

I have decided to "fill-in" the large cavity under voice coil path, and the i will make new measurements to see what would happen. I expect that the efficiency would rise, and that the notch would move towards higher frequency, may be 'out of the interest'.:(

After some problems, I have done, but notch remain, so now may be some experiments with phase-plug.....:crying:

[Legis]

Hi, has the back sticker of the 2446J changed at some point? In the attached pictures there are two different 2446J drivers (serial numbers 16992 and 01679). Their back stickers are little different from each other, the color is different and the little text reads "JBL incorporated ..." in the newer and "James B Lansing Sound..." in the older. I found that at least 2445J drivers had the "James B. Lansing..." text, but did also the first 2446Js had it and the sticker was changed at some point? If this is the case, I take there should not be significant (/any) changes in measured performance of different patches?

Regards,

Legis

[Mike F]

Hi, has the back sticker of the 2446J changed at some point? In the attached pictures there are two different 2446J drivers (serial numbers 16992 and 01679). Their back stickers are little different from each other, the color is different and the little text reads "JBL incorporated ..." in the newer and "James B Lansing Sound..." in the older. I found that at least 2445J drivers had the "James B. Lansing..." text, but did also the first 2446Js had it and the sticker was changed at some point? If this is the case, I take there should not be significant (/any) changes in measured performance of different patches?

Regards,

Legis

Have you measured or listened to the drivers?

[4313B]

Hi, has the back sticker of the 2446J changed at some point? In the attached pictures there are two different 2446J drivers (serial numbers 16992 and 01679). Their back stickers are little different from each other, the color is different and the little text reads "JBL incorporated ..." in the newer and "James B Lansing Sound..." in the older. I found that at least 2445J drivers had the "James B. Lansing..." text, but did also the first 2446Js had it and the sticker was changed at some point? If this is the case, I take there should not be significant (/any) changes in measured performance of different patches?

Regards,

LegisJBL dropped the whole James B. Lansing Sound thing years ago.

I suspect it finally got too costly to print all that out on everything.

[Legis]

Have you measured or listened to the drivers?

No I haven't but I will as soon as I get them.

[Mr. Widget]

I take there should not be significant (/any) changes in measured performance of different patches?There shouldn't be, but I'd be surprised if these two drivers measure identically. I have measured a number of used JBLs and depending on the life they have led, their performance can be all over the map.


Widget

[ivica]

There shouldn't be, but I'd be surprised if these two drivers measure identically. I have measured a number of used JBLs and depending on the life they have led, their performance can be all over the map.


Widget
I have almost the same experience with the old and 'older' used JBL drivers, that their responses are different, but generally (all measured with 2311 horn and 2308 lens) older diaphragms have some losses ( up to several dB-s) in the region from about 1.5kHz to about 3~4kHz, , and may be expectable over 10kHz. I vane no idea what are the reasons why mentioned losses happened. May some structural characteristics of titanium dome or suspension have changed over time, or over 'heavy" usage.
If it is assumed that the dome radius is near about 3 inch ( some calculation give "me" R=2 27/32"=72mm), that would lead to the maximal line over the dome mid-point of about 110mm what would, may be, correspond to wave length around 3.1kHz, and half wave length around 1.55kHz, but unfortunately, I have not seen any, technically acceptable, explanation of such "phenomena" .
May be some of the forum members have better explanation.

Regards
Ivica

[Legis]

Interesting, I hope the differences are not that great with my pair. I actually planned to use them with original phrams for the first few months in order to get to know the drivers, and then at some point change to beryllium phrams (Truextent), so the bigger factor is the mint looks than the condition of the original dia. My main concern was that the other one is a counterfeit driver, but I quess this is not the case.